For directional drilling, a drill bit at the end of a drill string is turned by a mud motor. The mud motor is powered by the flow of drilling mud that is pumped at the surface into the drill string and issues from the end of the drill string to clear cuttings from the well bore. Specifically, the mud motor may include a rotor coupled to the drill bit, and the flow of drilling mud through the mud motor may cause the rotor to rotate and drive the drill bit.
In certain instances, the drill bit and rotor may stop turning, causing the mud motor to stall. A mud motor stall may cause a blockage of the flow of drilling mud through the mud motor, which sends a pressure pulse back to the surface through the drilling mud. When a stall is detected during drilling, the drill string is retracted to free up the bit from the formation, and then drilling can be resumed. Frequent stalls can be addressed by adjusting drilling parameters such as the mud flow rate and the weight on the bit, the composition of the drilling mud, and the configuration of the bit.